A high dynamic range (HDR) display system may support displaying images that vary greatly in luminance levels from the palest areas to the darkest areas in the images. Under existing techniques, a luminance level of the darkest areas in an image may be reduced to a very dark level lower than an ordinary display panel may otherwise support, while a luminance level of the palest areas in the image may be set to a relatively high luminance. Accordingly, in a dark viewing environment with little ambient light, a viewer may be able to see images rendered with a large amount of details in various luminance levels and tonality.
Some display systems may also employ tone-mapping techniques to create a perception of, or to simulate, a high dynamic range by mapping tonality settings of an image and by enhancing local contrast values in adjacent portions of the image. For example, various portions in an original image may be made further darker or paler based on a complex tone-mapping algorithm to create an altered image, which is then rendered on a display panel.
Many existing techniques depend on a dark environment to exploit their HDR ability. However, in a wide range of ambient light conditions, many details, even if rendered by an existing HDR system, of an image may be imperceptible to a viewer who happens to be exposed to only moderate or high ambient light. For example, image details such as those with very low luminance levels cannot be properly perceived by the viewer. Particularly, portions that are of a luminance level of 0.5 nit or below may be masked by and become indistinct under the ambient light. Consequently, a display system that implements a high dynamic range and/or tone mapping, at a great cost to a consumer/viewer, may in the end be limited to viewing environments only with little ambient light. Indeed, the HDR system may look even worse than a regular display system in many ambient light conditions, because of the former's susceptibility of losing details in such conditions.
Many existing techniques such as tone-mapping require complicated processing of large volumes of image data. Thus, such techniques have a tendency to be quite expensive to implement, but at the same time are limited to relatively ideal viewing environments.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, issues identified with respect to one or more approaches should not assume to have been recognized in any prior art on the basis of this section, unless otherwise indicated.